Two identical balls roll across the top of a table on parallel paths. One of the balls has to roll down into and up out of a dip in the table. The other ball rolls on the flat all the time. Which ball gets to the far side of the table first, and why?.

First Law of Motion:"A body persists in a state of rest or of uniform motion unless acted upon by an external force."

The body (ball) is in uniform motion which is not impeded in its forward direction. That motion is influenced by gravity being perpendicular to the forward motion but puts no restriction upon the forward velocity.